Theresa May describes sadness over sacking of close friend Damian Green

Theresa May has spoken of her deep personal sadness at being forced to sack her close friend Damian Green, but emphasised she expected the highest standards of ministers and that victims of sexual harassment should be able to feel safe speaking out.

The report, which also examined his conduct towards Conservative activist Kate Maltby, found his statements about the computer were inaccurate and misleading.

May’s comments came as several Conservative MPs lambasted the Metropolitan police detectives, now retired, who discovered the pornography during a raid on Green’s Commons office connected to a separate leaks inquiry in 2008.

The pair now face investigation over whether they breached data protection legislation after the Metropolitan police commissioner, Cressida Dick, said the force had referred them to the Information Commissioner’s Office.

Green, a friend of May’s for 40 years, was made her first secretary of state after the June election. He was viewed as her closest cabinet ally after the departure of her trusted aides Nick Timothy and Fiona Hill following the disastrous election campaign.

May was heading for Cyprus, where she was visiting British troops on a final political engagement before Christmas.

“He and I have known each other since university and he’s a good – was a good – minister,” May said. “He’s obviously been a minister in a number of areas; he and I worked together in the Home Office before I became prime minister.”

In her letter to Green on Wednesday, May said she had asked him to resign “with deep regret and enduring gratitude”.

Green was ruled to have twice breached the ministerial code, because his misleading comments had fallen short of the “seven principles of public life”, one of which is honesty.

But while May used a press conference in Warsaw to reiterate her belief that the conduct of the officers should be “properly looked at”, on the plane she stressed the inevitability of Green’s departure after she requested a second opinion from Sir Alex Allan, her independent adviser on ministers’ interests.

“For me what was important was obviously the cabinet secretary’s report, which was endorsed by Sir Alex Allan, was clear that there had been breaches of the ministerial code. I think it’s important we uphold the highest standards in public life,” May said.

The cabinet secretary’s report found that Maltby’s account of her meeting with Green, where she had alleged he had propositioned her in exchange for help with her career, was “plausible”, but “with competing and contradictory accounts of what were private meetings, it is not possible to reach a definitive conclusion”.

Maltby told BBC news that she had informed Downing Street of Green’s behaviour “frequently, consistently and contemporaneously”, insisting May knew about the sexual harassment complaints before she made Green her de facto deputy.

She added that she had never sought Green’s resignation, but instead wanted to challenge parliament’s sexualised working environment, adding “coming forward was a calculated loss, because there’s something more important at stake”.

Asked if May herself and the Conservative party owed Maltby an apology, the prime minister said it was Green’s responsibility and said he had done so in his letter. “He recognised that although there might have been a different view as to what had happened, he regretted any distress that had been caused, and he did apologise to her. I think that was absolutely right,” she said.

In his letter, Green said: “I deeply regret the distress caused to Kate Maltby following her article about me and the reaction to it. I do not recognise the events she described in her article, but I clearly made her feel uncomfortable and for this I apologise.”

Maltby, a writer and fellow at the liberal Tory thinktank Bright Blue, was attacked in a piece in the Daily Mail shortly after she went public against Green in an article for the Times, where she was called “one pushy lady” and it was suggested her parents were “aghast at what Kate had done”. After the report was published on Wednesday, Maltby’s parents issued a public statement vehemently denying the claims.

Asked if she was concerned Maltby had been wrongly villified by the press, May avoided speaking about the article directly, only saying it was “an important issue ... ensuring people do feel they are able to bring forward any concerns and those will be treated seriously and looked into”.

May is expected to wait until the new year before announcing a replacement for Green, which some Conservative MPs now anticipate could be part of a wider reshuffle to reinvigorate her cabinet, and promote newer Commons entrants to junior posts.

Asked when Green might be replaced, May’s spokesman in London said it would not happen before parliament went into recess on Thursday evening.

Green is a generally popular figure among his fellow Tory MPs. The foreign secretary, Boris Johnson, who is visiting Moscow, described Green as “a fine public servant” and predicted he might return to the government in the future.

Johnson echoed the view of some other Conservative MPs by saying Green appeared to have been the victim of a “vendetta” by the former police officers, Bob Quick and Neil Lewis, calling the apparent leak of information from the 2008 raid to the media “a bit whiffy”.

Despite May asking him to resign, Green will receive a payoff of nearly £17,000, the Cabinet Office has confirmed.